1. Field
The field includes ion storage materials, and in particular nanoscale ion storage materials useful in devices such as batteries.
2. Summary of Related Art
Ion storage materials are widely employed in storage batteries and other electrochemical devices. Various ion storage materials are known, including alkaline transition metal phosphates. This class of compounds can crystallize in a number of structure types. Examples include ordered or partially disordered structures of the olivine (AxMXO4), NASICON (Ax(M′,M″)2(XO4)3), VOPO4, LiVPO4F, LiFe(P2O7) or Fe4(P2O7)3 structure types, wherein A is an alkali ion, and M, M′ and M″ are metals. Amorphous FePO4 materials, prepared in the delithiated state, also have been used as lithium storage materials (Okada et al., Patent Abstracts of Japan Publication No. 06-283207). Amorphous materials including lithium cobalt phosphate also have been described (U.S. Pat. No. 5,705,296).
Many of the above ion storage compounds have relatively low electronic conductivity and alkali ion conductivity, which are less than ideal for electrochemical applications. Many such compounds also exhibit limited solid solution range. For example, LiFePO4 has been widely reported in the scientific literature to have an extremely limited range of solid solution at room temperature.
“Nanocrystalline” ion storage materials have been reported in the literature. For example, Prosini et al. in “A New Synthetic Route for Preparing LiFePO4 with Enhanced Electrochemical Performance,” J. Electrochem. Soc., 149:A886-A890 (2002), describe LiFePO4 of 8.95 m2/g specific surface area as nanocrystalline. However, these materials, while somewhat improved, have not been of sufficiently small size scale to provide substantially different properties compared to their larger scale counterpart conventional ion storage materials. Further nanoscale particulate phosphate materials also have been disclosed (US 2002/0192137).
Lithium transition metal phosphate storage compounds useful in high energy, high power batteries are described in U.S. Patent Application Publication No. US2004/0005265, entitled “Conductive Lithium Storage Electrode,” and U.S. patent application Ser. No. 11/396,515, entitled “Nanoscale Ion Storage Materials,” now U.S. Pat. No. 7,939,201, the disclosures of which are incorporated herein by reference.